lecture 27 Flashcards
what were the first organisms on the earth and how long have they been here
the first were bacteria, they first developed on earth 3.8 billion years ago
describe the bacterial genome
typically a single circular genome that is not contained within a nuclear envelope
whats a nucleoid
nucleoid is the region of the cytoplasm that the genome of the bacteria is suspended in
what are plasmids
other genomic sequences that are free in the cytoplasm and are separate from the whole genome.
about how many genes are contained in the bacterial genome
about 500
why does the small genome support the idea they were on earth first
as their genome is much shorter and more specialised. so they have evolved to produce less unnecessary DNA
what do archaea and bacteria not have
membrane-bound organelles or a nuclear envelope
what are the functions of the bacterial cell wall
its a macromolecule layer that provides strength to the cell
and it protects the cell against lysing and confers the cell shape
what are mycoplasmas
prokaryotes that lack a cell wall, they are a group of pathogenic bacteria
whats the main component of the bacterial cell wall
peptidoglycan
whats the structure of the peptidoglycan fibres
a chain of NAM and NAG molecules
what does tetrapeptide do
it vertically links the peptidoglycan chains
what peptidoglycan component is the tetrapeptide on
its on the NAM molecule
what are the peptidoglycan chains joined by
they are joined via amino acid cross bridges which links to the tetrapeptides
what enzyme catalyses the cross linking of the tetrapeptides
this is transpeptidase
what enzyme does penicillin target
the transpeptidase
what does penicillin do?
blocks the transpeptidase, so the cross-linking of the cell wall doesnt occur, so when in liquid media the cells lyse and die
what do the gram stains mean
gram stain blue is positive for peptidoglycan in the cells wall. gram stain pink is negative for peptidoglycan.
describe gram stain process
Firstly crystal violet is added to sample. Then iodine is added, which acts as a mordant, fixing the stain to the cell wall. You then add alcohol to wash away the crystal violet. Then apply safranin, counterstain, see what colour the thing goes.
how thick is the cell wall of peptidoglycan if present
20-80nm
why is positive blue
because the initial crystal violet is absorbed by peptidoglycan layers and doesn;t get washed by the alcohol
describe structure of gram positive cells
they have a thick layer of peptidoglycan on the outside of their cell membrane
structure of gram negative cells
they have a thin layer of peptidoglycan, 5-10nm between the plasma membrane and an outer membrane.
what does flagella do
The flagellum rotates, this rotation allows the bacteria to move in liquid media
what are the flagella made of
These flagella are made of proteins and are rather small, having a 10-20 nm diameter.
what are the three components of the flagella, describe them
There are 3 major functions of the flagella:
Long filament: extends into the medium which the cell is suspended in, this part is composed of subnits of flagellin protein
Hook: curved section connecting the long filament to the cell surface
Basal body: anchors the flagellum into the cell membrane by plates
the bacterial cells do what movement type, and whats different to other things in this taxis
chemotaxis, they are too small to notice spactial gradients, instead they use temporal gradients.
what are fimbriae
Function: Structures with adhesive properties that
cause bacteria to stick/adhere to surfaces, Much shorter and more numerous than flagella “hairlike”, 100-1000/cell and 2-8 nm in diameter. 1 µM in
length
do all cells have fimrbiae and how do they help the bacteria
Not all bacteria posses these, it is more an inherited trait as they are passsed on from parent cells when its need.
These have receptors to tell what environment they are colonising. so they are only present in bacteria which need to be present and stuck to specific area
whats a special type of fimbriae
the sex pilus
whats the sex fimbriae and whats it do
Massive protein structure, connecting two bacterial cells.
The connection of two cells ios a conjugative pilus.
They use this to trransfer DNA from one cell to another in a process called conjugation.
Conjugation is a form of horizontal gene transfer.
whats glycocalyx
A gelatinous polysaccharide and or polypeptide covering the outer side of the cell.
This forms a sticky meshwork of fibres
whats a capsule
An organised defined structure attached firmly to cell wall
whats a slime layer
Glycocalyx disorganised without cell shape, attached loosely to cell wall
capsules serve what purpose
Bacteria will capsule are hard to eradicate.
Capsules are Virulence factors- protecting bacteria from phagocytosis and being engulfed by immune cells.
Also prevent dessication
why do bacteria form endospores and when
These are formed during unfavourable growth conditions. so too low nutrients and too high bacteria density. These protect cells from stress, only two types of bacteria do this
endospores only form for what
gram postive cells
whats a virulence factor
protecting bacteria
from phagocytosis and engulfment by
immune cells.
